Antenna devices that transmit electromagnetic waves to an arbitrary direction by some methods such as providing a plurality of antennas have hitherto been utilized.
The phased-array radar device shown in Patent Literature 1, for example, changes the overall directivity of the electromagnetic waves transmitted from antennas by changing the phases of electromagnetic waves emitted from the antennas, with a transmitter module that includes an amplifier and a high-frequency phase shifter connected to each of the antennas.
However, high-precision high-frequency phase shifters are generally large and expensive. Accordingly, an antenna device that uses a transmitter module having such a high-frequency phase shifter and is capable of precisely controlling the overall directivity of electromagnetic waves transmitted from the antennas is large as well as expensive.
A wireless communication system shown, for example, in Patent Literature 1 has hitherto been proposed as a high-frequency transmitter. Such a wireless communication system includes a converter that converts electrical energy to high-frequency power, a high-frequency power transmission means that sends the converted high-frequency power to a transmitter, and the transmitter that converts the high-frequency power sent thereto to an electromagnetic wave and transmits the converted electromagnetic wave to the outside. The high-frequency electromagnetic wave is an electromagnetic wave of 10 GHz or more, for example. The high-frequency power transmission means is a waveguide, for example. The transmitter is an antenna, for example. In the wireless communication system shown in Patent Literature 1, a transceiver device corresponds to the converter, an RF coaxial cable corresponds to the high-frequency power transmission means, and an antenna corresponds to the transmitter.
With this configuration, electrical energy supplied from a power supply is converted to high-frequency power by the converter. The high-frequency power is sent to the transmitter by the high-frequency power transmission means, and converted into an electromagnetic wave and transmitted to the outside by the transmitter, whereby communication among a plurality of devices spaced away from each other is made possible.
The converter commonly requires parts such as capacitors, coils, quartz oscillators, and semiconductor elements. These parts are mounted on a circuit board and turned into a board unit to be installed. When designed as a board unit, the converter has less space for installing antennas, so that the converter and antennas are commonly spaced away from each other. This is why the high-frequency power transmission means is required for transmission between the converter and the antennas that are spaced away from each other, so that a waveguide or the like is used.
However, transmission of high-frequency power by a high-frequency power transmission means such as an RF coaxial cable and waveguide as in the wireless communication system shown in Patent Literature 1 noted above significantly attenuates the high-frequency power, which reduces the overall efficiency of the system.